Method of manufacturing SOI substrate

ABSTRACT

To provide an SOI substrate with an SOI layer that can be put into practical use, even when a substrate with a low allowable temperature limit such as a glass substrate is used, and to provide a semiconductor substrate formed using such an SOI substrate. In order to bond a single-crystalline semiconductor substrate to a base substrate such as a glass substrate, a silicon oxide film formed by CVD with organic silane as a source material is used as a bonding layer, for example. Accordingly, an SOI substrate with a strong bond portion can be formed even when a substrate with an allowable temperature limit of less than or equal to 700° C. such as a glass substrate is used. A semiconductor layer separated from the single-crystalline semiconductor substrate is irradiated with a laser beam so that the surface of the semiconductor layer is planarized and the crystallinity thereof is recovered.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an SOI (silicon on insulator)substrate. In addition, the present invention relates to a semiconductordevice manufactured using the SOI substrate.

Note that a semiconductor device in this specification refers to alldevices that can function by utilizing semiconductor characteristics.For example, electro-optic devices, semiconductor circuits, andelectronic devices all fall into the category of a semiconductor device.

2. Description of the Related Art

An integrated circuit that uses a semiconductor substrate called an SOIsubstrate, which is provided with a thin single-crystallinesemiconductor layer on an insulating surface, has been developed,replacing a silicon wafer formed by cutting an ingot of asingle-crystalline semiconductor into thin slices. Using an SOIsubstrate can reduce parasitic capacitance between a drain of atransistor and a substrate. Therefore, the SOI substrate has beendrawing attention as a means of improving the performance of asemiconductor integrated circuit.

Among methods of manufacturing SOI substrates, there is known a hydrogenion delamination method (also called a Smart Cut® method in some cases)(for example, see Reference 1: U.S. Pat. No. 6,372,609). The method offorming an SOI in Reference 1 includes the steps of implanting hydrogenions into a silicon wafer to form a fine bubble layer at a position of apredetermined depth from the surface, and then bonding thehydrogen-ion-implanted silicon wafer to another silicon wafer with asilicon oxide film interposed therebetween. After that, heat treatmentis applied to delaminate the hydrogen-ion-implanted wafer in a thin-filmform, with the fine bubble layer used as a cleavage plane. The hydrogenion delamination method is also called a Smart Cut® method in somecases.

However, a damage layer produced due to the hydrogen ion implantationremains on the surface of the SOI wafer after the delamination. InReference 1, a method of removing the damage layer is disclosed. InReference 1, after the delamination step, an oxide film is formed on thesurface of the SOI substrate by heat treatment in an oxidizingatmosphere. Then, the oxide film is removed and heat treatment of 1000to 1300° C. is applied in a reducing atmosphere.

Also, there is known an SOI substrate which is obtained by bonding asilicon layer separated from a silicon wafer to a glass substrate (forexample, see Reference 2: Japanese Published Patent Application No.2004-087606 and Reference 3: Japanese Published Patent Application No.H11-163363).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an SOI substrateformed using a substrate with a low allowable temperature limit such asa glass substrate which is used in the manufacture of liquid crystalpanels. It is another object of the present invention to provide asemiconductor device formed using such an SOI substrate.

In order to manufacture an SOI substrate, a layer that smoothesirregularities of a surface of a semiconductor substrate and has ahydrophilic surface is provided as the bonding layer. As an example ofthe bonding layer, a silicon oxide film formed by CVD (chemical vapordeposition) using organic silane as a silicon source gas is employed.Examples of an organic silane gas include compounds containing siliconsuch as tetraethoxysilane (abbreviation: TEOS, chemical formula:Si(OC₂H₅)₄), trimethylsilane (TMS: (CH₃)₃SiH),tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane(OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (SiH(OC₂H₅)₃), ortrisdimethylaminosilane (SiH(N(CH₃)₂)₃).

The top surface of a semiconductor layer of an SOI substrate hasirregularities generated by separation from the semiconductor substrate,and thus has low planarity. Therefore, the top surface is irradiatedwith a laser beam in order to have improved planarity. By the laserirradiation, irregularities of the top surface of the semiconductorlayer generated by separation from the semiconductor substrate can bemelted and solidified, so that the top surface of the semiconductorlayer can be planarized.

Forming a bonding layer allows the semiconductor layer to be separatedfrom the semiconductor substrate and to be fixed on a base substrate, ata temperature of less than or equal to 700° C. Even if the basesubstrate is a glass substrate or the like which has an allowabletemperature limit of less than or equal to 700° C., an SOI substratewith a strong bonding plane can be formed.

Various glass substrates used in the electronics industry can beemployed as the base substrate on which the semiconductor layer isfixed. For example, alkali-free glass such as aluminosilicate glass,aluminoborosilicate glass, or barium borosilicate glass can be used.That is, a single-crystalline semiconductor layer can be formed over asubstrate which is over 1 meter on a side. With such a large-areasubstrate, not only a display device such as a liquid crystal displaybut also a wide variety of other semiconductor devices can bemanufactured.

In addition, the semiconductor layer separated from the semiconductorsubstrate can be planarized by the laser irradiation. Further, thecrystallinity of the semiconductor layer can be recovered by the laserirradiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating the structure of an SOIsubstrate;

FIG. 2 is a cross-sectional view illustrating the structure of an SOIsubstrate;

FIG. 3 is a cross-sectional view illustrating the structure of an SOIsubstrate;

FIGS. 4A to 4C are cross-sectional views illustrating a method ofmanufacturing an SOI substrate;

FIGS. 5A and 5B are cross-sectional views illustrating a method ofmanufacturing an SOI substrate;

FIGS. 6A to 6C are cross-sectional views illustrating a method ofmanufacturing an SOI substrate;

FIGS. 7A and 7B are cross-sectional views illustrating a method ofmanufacturing an SOI substrate;

FIGS. 8A to 8E are cross-sectional views illustrating a method ofmanufacturing a semiconductor device using an SOI substrate;

FIGS. 9A and 9B are cross-sectional views illustrating a method ofmanufacturing a semiconductor device using an SOI substrate;

FIG. 10 is a block diagram illustrating the configuration of amicroprocessor manufactured using an SOI substrate;

FIG. 11 is a block diagram illustrating the configuration of an RFCPUmanufactured using an SOI substrate;

FIGS. 12A to 12H are cross-sectional views illustrating a method ofmanufacturing an SOI substrate of Example 1;

FIGS. 13A to 13D are IPF maps of single-crystalline silicon layersobtained from EBSP;

FIG. 14A is a graph showing the Raman shift peak wavenumber ofsingle-crystalline silicon layers vs. laser energy density, and FIG. 14Bis a graph showing the FWHM (full width at half maximum) of the Ramanspectra of single-crystalline silicon layers vs. laser energy density;

FIG. 15 shows observed images of surfaces of single-crystalline siliconlayers, which include dark-field images observed with an opticalmicroscope and images observed with an atomic force microscope (AFMimages), and also illustrates surface roughness calculated from the AFMimages;

FIG. 16 is an energy diagram of hydrogen ion species;

FIG. 17 is a graph showing the results of ion mass spectrometry;

FIG. 18 is a graph showing the results of ion mass spectrometry;

FIG. 19 is a graph showing the profile (calculated values and measuredvalues) of hydrogen in the depth direction when the accelerating voltageis 80 kV;

FIG. 20 is a graph showing the profile (calculated values, measuredvalues, and fitting functions) of hydrogen in the depth direction whenthe accelerating voltage is 80 kV;

FIG. 21 is a graph showing the profile (calculated values, measuredvalues, and fitting functions) of hydrogen in the depth direction whenthe accelerating voltage is 60 kV;

FIG. 22 is a graph showing the profile (calculated values, measuredvalues, and fitting functions) of hydrogen in the depth direction whenthe accelerating voltage is 40 kV; and

FIG. 23 is a list of fitting parameters of the fitting function shown inFIGS. 20 to 22 (hydrogen atom ratios and hydrogen ion species ratios).

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Mode

The present invention will be described hereinafter. Note that it willbe easily understood by those skilled in the art that the presentinvention can be embodied in a wide variety of different ways and,therefore, various modifications and variations can be made to thepresent invention without departing from the spirit and scope thereof.Thus, the present invention should not be construed as being limited tothe description in the following embodiment mode and example.

FIG. 1 is a cross-sectional view illustrating an exemplary structure ofan SOI substrate. In FIG. 1, reference numeral 100 denotes a basesubstrate; 102, a semiconductor layer; and 104, a first bonding layer.In the SOI substrate in FIG. 1, the semiconductor layer 102 is fixed tothe base substrate 100 by bonding between the first bonding layer 104and the base substrate 100.

The base substrate 100 can be any of a substrate made of an insulatingmaterial, a semiconductor substrate made of a semiconductor material,and a substrate made of a conductive material. The base substrate 100can be a substrate with an allowable temperature limit of less than orequal to 700° C. Specifically, various glass substrates used in theelectronics industry, such as aluminosilicate glass, aluminoborosilicateglass, or barium borosilicate glass can be employed as the basesubstrate 100. Further, a substrate with an allowable temperature limitof over 700° C. can also be used for the base substrate 100, forexample, a quartz substrate, a sapphire substrate, a semiconductorsubstrate such as a silicon wafer, a ceramic substrate, a stainlesssteel substrate, a metal substrate, or the like can be used.

The semiconductor layer 102 is a layer formed by being separated from asemiconductor substrate. For the semiconductor substrate, asingle-crystalline semiconductor substrate is mostly desirably used, buta polycrystalline semiconductor substrate can also be used. Aconstituent semiconductor of the semiconductor layer 102 is silicon,silicon-germanium, or germanium. Alternatively, the semiconductor layer102 can be made of a compound semiconductor such as gallium arsenide orindium phosphide. The thickness of the semiconductor layer 102 can be inthe range of from 5 to 500 nm, and is preferably in the range of from 10to 200 nm.

The first bonding layer 104 is formed between the base substrate 100 andthe semiconductor layer 102. The first bonding layer 104 is a layerformed on a surface of a semiconductor substrate which is used forformation of the semiconductor layer 102. The first bonding layer 104preferably has a hydrophilic property, and a silicon oxide film issuitable for the first bonding layer 104. It is particularly preferableto use a silicon oxide film which is formed by chemical vapor deposition(CVD) using organic silane as a silicon source gas. An oxygen gas (O₂gas) can be used as an oxygen source gas used for formation of thesilicon oxide film. Alternatively, the first bonding layer 104 can beformed by depositing a silicon oxynitride film by plasma CVD using atleast monosilane and NO₃ as a source gas or by depositing a siliconnitride oxide film by plasma CVD using at least monosilane, NH₃, and NO₃as a source gas. Further, the first bonding layer 104 can also be formedby depositing aluminum oxide by sputtering or by oxidizing thesemiconductor substrate.

The thickness of the first bonding layer 104 is preferably in the rangeof from 5 to 500 nm. Such a thickness allows the formation of the firstbonding layer 104 being capable of forming a bond and having a smoothsurface. In addition, such a thickness can ease the distortion of thefirst bonding layer 104 with the base substrate 100 bonded thereto.

For the organic silane gas, the following compounds containing siliconcan be used: tetraethoxysilane (TEOS, chemical formula: Si(OC₂H₅)₄),tetramethylsilane (TMS, chemical formula: Si(CH₃)₄),tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane(OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (SiH(OC₂H₅)₃),trisdimethylaminosilane (SiH(N(CH₃)₂)₃), and the like.

In the SOI substrate in FIG. 1, the base substrate 100 may also beprovided with a similar bonding layer to the first bonding layer 104.For example, when silicon oxide, which is deposited by CVD using organicsilane as a source material, is used as the material of one of thesurfaces being to form a bond, a strong bond can be formed.

FIG. 2 is a cross-sectional view illustrating an exemplary structure ofan SOI substrate. In FIG. 2, reference numeral 100 denotes a basesubstrate; 102, a semiconductor layer; 104, a first bonding layer; 105,an insulating layer; and 106, a second bonding layer. In the SOIsubstrate in FIG. 2, the semiconductor layer 102 is fixed to the basesubstrate 100 by bonding between the first bonding layer 104 and thesecond bonding layer 106.

The insulating layer 105 is made of a single-layer film or a multi-layerfilm having a stack of two or more layers. The insulating layer 105includes at least one insulating film containing nitrogen and silicon,such as a silicon nitride film or a silicon nitride oxide film, whichcan prevent the semiconductor layer 102 from being contaminated bymobile ion impurities such as alkali metal or alkaline earth metal beingto diffuse into the semiconductor layer 102 from the glass substrateused as the base substrate 100. Note that instead of the insulatinglayer 105, a conductive layer such as metal or a metal compound or asemiconductor layer such as amorphous silicon can also be formed.

The second bonding layer 106 is a film formed over the base substrate100, and is preferably a film formed from the same material as the firstbonding layer, that is a silicon oxide film. For the second bondinglayer 106, a silicon oxide film, which is formed by CVD using an organicsilane gas as a silicon source gas, can be used similarly to the firstbonding layer 104. It is also possible to use a silicon oxide filmformed using a different gas from organic silane, as the silicon sourcegas. Note that the second bonding layer 106 may be formed on the basesubstrate 100 without forming the insulating layer 105.

In FIG. 2, an insulating film, a semiconductor film, or a conductivefilm may be formed between the insulating layer 105 and the basesubstrate 100. Such a film can be either a single-layer film or amulti-layer film. Also, in FIG. 2, an insulating film, a semiconductorfilm, or a conductive film may be formed between the insulating layer105 and the second bonding layer 106. Such a film can be either asingle-layer film or a multi-layer film.

In FIG. 2, the insulating layer 105 can be omitted. In that case, aninsulating film, a semiconductor film, or a conductive film may beformed between the second bonding layer 106 and the base substrate 100.Such a film can be either a single-layer film or a multi-layer film. Inaddition, in FIG. 2, the second bonding layer 106 can be omitted. Inthat case, the semiconductor layer 102 is fixed to the base substrate100 by bonding between the first bonding layer 104 and the insulatinglayer 105 to each other.

FIG. 3 is a cross-sectional view illustrating an exemplary configurationof an SOI substrate. In FIG. 3, reference numeral 100 denotes a basesubstrate; 102, a semiconductor layer; 104, a first bonding layer; and120, an insulating layer. In the SOI substrate in FIG. 3, thesemiconductor layer 102 is fixed to the base substrate 100 by bondingbetween the first bonding layer 104 and the base substrate 100.

The insulating layer 120 is a layer formed on a side of a semiconductorsubstrate from which the semiconductor layer 102 separated. Thesemiconductor layer 102 has a single-layer structure or a stacked-layerstructure. The insulating layer 120 preferably includes at least oneinsulating film containing at least nitrogen. Examples of an insulatingfilm containing nitrogen include a silicon nitride film and a siliconnitride oxide film. The formation of a silicon nitride film or a siliconnitride oxide film can prevent impurities such as mobile ions ormoisture from diffusing into and contaminating the semiconductor layer102.

For the insulating layer 120, a film with any of the followingstructures can be used, for example: a two-layer insulating filmobtained by sequentially stacking a silicon oxynitride film and asilicon nitride oxide film over the semiconductor layer 102, a two-layerinsulating film obtained by sequentially stacking a silicon oxide filmand a silicon nitride oxide film over the semiconductor layer 102, atwo-layer insulating film obtained by sequentially stacking a siliconoxide film and a silicon nitride film over the semiconductor layer 102,or a single-layer insulating film made of silicon nitride.

Note that silicon oxynitride means a substance that contains more oxygenthan nitrogen. For example, silicon oxynitride includes oxygen,nitrogen, silicon, and hydrogen at concentrations ranging from 55 at. %to 65 at. %, 1 at. % to 20 at. %, 25 at. % to 35 at. %, and 0.1 at. % to10 at. %, respectively. Also, silicon oxynitride includes oxygen,nitrogen, silicon, and hydrogen at concentrations ranging from 50 at. %to 70 at. %, 0.5 at. % to 15 at. %, 25 at. % to 35 at. %, and 0.1 at. %to 10 at. %, respectively. Further, silicon nitride oxide means asubstance that contains more nitrogen than oxygen. For example, siliconnitride oxide includes oxygen, nitrogen, silicon, and hydrogen atconcentrations ranging from 15 at. % to 30 at. %, 20 at. % to 35 at. %,25 at. % to 35 at. %, and 15 at. % to 25 at. %, respectively. Also,silicon nitride oxide includes oxygen, nitrogen, silicon, and hydrogenat concentrations ranging from 5 at. % to 30 at. %, 20 at. % to 55 at.%, 25 at. % to 35 at. %, and 10 at. % to 30 at. %, respectively.

Next, a method of manufacturing the SOI substrate illustrated in FIG. 1will be described with reference to FIGS. 4A to 5B. FIGS. 4A to 5B arecross-sectional views for illustrating the method of manufacturing theSOI substrate.

As illustrated in FIG. 4A, a semiconductor substrate 101 is prepared.The semiconductor layer 102 is formed from a section of thesemiconductor substrate 101. The semiconductor substrate 101 can be asingle-crystalline semiconductor substrate. Examples of asingle-crystalline semiconductor substrate include a single-crystallinesilicon substrate, a single-crystalline silicon-germanium substrate, asingle-crystalline germanium substrate, and the like. A polycrystallinesemiconductor substrate can also be used instead of thesingle-crystalline semiconductor substrate. Further, asingle-crystalline semiconductor substrate or a polycrystallinesemiconductor substrate made of a compound semiconductor such as galliumarsenide or indium phosphide can be used.

First, the semiconductor substrate 101 is cleaned by washing. Next, asource gas is excited (plasma of the source gas is generated) togenerate ion species. Then, the ion species generated from the sourcegas are accelerated with an electric field, producing an ion flux 125.The single-crystalline semiconductor substrate is irradiated with theion flux 125 as illustrated in FIG. 4A. Ions included in the ion flux125 are implanted to a region of a predetermined depth from the surfaceof the semiconductor substrate 101, whereby an ion-implanted layer 103is formed. The depth at which ions are implanted is determined by takinginto account the thickness of the semiconductor layer 102 to be fixed onthe base substrate 100. The thickness of the semiconductor layer 102 canbe in the range of from 5 to 500 nm, and is preferably in the range offrom 10 to 200 nm. The accelerating voltage of the ion flux 125 iscontrolled by taking into account the thickness of the semiconductorlayer 102 so that the ion-implanted layer 103 can be formed at apredetermined depth. This ion implantation process is a process in whichan element including ion species is introduced into the semiconductorsubstrate 101 by irradiating the semiconductor substrate 101 with theion flux 125 including accelerated ion species. Therefore, theion-implanted layer 103 is a region to which an element including ionspecies is introduced. In addition, the ion-implanted layer 103 is alsoa layer whose crystal structure is lost and weakened by the impact ofthe accelerated ion species (an embrittlement layer).

In order to implant ions to the semiconductor substrate 101, an ionimplantation apparatus, which mass-separates ion species generated froman excited process gas and implants ion species with a predeterminedmass, can be used. Alternatively, an ion doping apparatus, whichimplants all ion species generated from a process gas without massseparation, can be used.

A source gas used for forming the ion-implanted layer 103 can be one ormore of a hydrogen gas, a noble gas such as helium or argon, a halogengas typified by a fluorine gas, and a halogen compound gas such as afluorine compound gas (for example, BF₃).

H⁺, H₂ ⁺, and H₃ ⁺ are produced from a hydrogen gas (H₂ gas). When ahydrogen gas is used as a source gas, the gas is preferably implantedinto the semiconductor substrate 101 such that the semiconductorsubstrate 101 contains the highest percentage of H₃ ⁺. Implanting the H₃⁺ ions can increase the efficiency of injection and shorten theimplantation time. Further, separation of the semiconductor layer fromthe semiconductor substrate 101 becomes easy. It is easier to generateH₃ ⁺ ions from a hydrogen gas with an ion doping apparatus than with anion implantation apparatus. In the case of using an ion dopingapparatus, it is preferable to generate the ion flux 125 in which thepercentage of H₃ ⁺ ions to the total amount of H⁺, H₂ ⁺, and H₃ ⁺ isgreater than or equal to 70%, or more preferably greater than or equalto 80%. In order to form the ion-implanted layer 103 in a shallowregion, the ion accelerating voltage needs to be set low. However,atomic hydrogen (H) can be efficiently added to the semiconductorsubstrate 101 by increasing the percentage of H₃ ⁺ ions in the plasmathat is generated by excitation of the hydrogen gas. This is because,since the mass of an H₃ ⁺ ion is three times much as an H⁺ ion, theaccelerating voltage of the H₃ ⁺ ion can be tripled compared to that ofthe H⁺ ion in the case where one hydrogen atom is added at the samedepth. When the ion accelerating voltage can be increased, the tact timeof the ion irradiation step can be reduced, whereby productivity andthroughput can be improved.

When a noble gas, which is a monatomic gas and is composed of one kindof element, is used as a source gas, ions species with the same mass canbe implanted into the semiconductor substrate 101 without massseparation. Therefore, the depth at which the ion-implanted layer 103 isformed can be easily controlled.

In addition, the ion-implanted layer 103 can be formed by conducting aplurality of ion-implantation steps. In that case, either the sameprocess gas or a different process gas may be used in each ion-addingstep. Described here is an example in which the ion-implanted layer 103is formed through two ion-adding steps.

For example, ions are implanted using a noble gas as a source gas. Next,ions are implanted using a hydrogen gas as a process gas. It is alsopossible to implant ions using a halogen gas or a halogen compound gasand then implant ions using a hydrogen gas. In the case of implantingion species including fluorine, a F₂ gas or a BF₃ gas can be used.

In order to form the ion-implanted layer 103, it is necessary to implantions to the semiconductor substrate 101 with a high dosage condition,but this could result in a rough surface of the semiconductor substrate101. Therefore, a protective film for protecting the surface of thesemiconductor substrate 101 is preferably formed to a thickness of from50 to 200 nm by depositing a silicon nitride film, a silicon nitrideoxide film, or the like on the surface of the semiconductor substrate101.

Next, as illustrated in FIG. 4B, the first bonding layer 104 is formedon a surface to be bonded to the base substrate 100. Here, a siliconoxide film is formed as the first bonding layer 104. The silicon oxidefilm is preferably formed by CVD using an organic silane gas as asilicon source gas. Examples of a silicon source gas include SiH₄,Si₂H₆, SiCl₄, SiHCL₃, SiH₂Cl₂, SiH₃Cl₃, and SiF₄ as well the organicsilane gas. As an oxygen source gas for forming this silicon oxide film,an oxygen gas can be used. In addition, the CVD can be either plasma CVDor low-pressure CVD.

In the step of forming the first bonding layer 104, the heatingtemperature of the semiconductor substrate 101 is preferably atemperature at which an element or a molecule that has been implanted tothe ion-implanted layer 103 does not escape, that is a temperature atwhich gas does not escape of the ion-implanted layer 103. The heatingtemperature is preferably less than or equal to 350° C. Therefore,plasma CVD is preferably used for forming the first bonding layer 104.Note that the heat treatment temperature for separating thesemiconductor layer from the semiconductor substrate 101 is higher thanthe deposition temperature of the first bonding layer 104.

In the case of forming the SOI substrate in FIG. 3, the insulating layer120 is formed before the formation of the first bonding layer 104. Forexample, in order to form a silicon nitride film, plasma CVD may beperformed using SiH₄ and NH₃ as a process gas. In addition, in order toform a silicon oxynitride film or a silicon oxide film, plasma CVD maybe performed using SiH₄ and N₂O as a process gas. Further, when thesemiconductor substrate 101 is a silicon substrate, a silicon nitridefilm (or a silicon oxide film) can be formed by nitriding (or oxidizing)the semiconductor substrate 101. In that case, by nitriding andoxidizing the semiconductor substrate 101, a silicon nitride oxide filmor a silicon oxynitride film can be formed.

The insulating layer 120 can be formed before or after the formation ofthe ion-implanted layer 103. When the heating temperature required forforming the insulating layer 120 is a temperature at which gas couldescape of the ion-implanted layer 103, the insulating layer 120 isformed before the formation of the ion-implanted layer 103.

FIG. 4C is a cross-sectional view illustrating the step of bonding thebase substrate 100 and the first bonding layer 104 to each other bybringing the base substrate 100 and the semiconductor substrate 101,which has the first bonding layer 104 formed on its surface, into closecontact with each other. First, surfaces of the base substrate 100 andthe first bonding layer 104 that will form a bonding interface arewashed by ultrasonic cleaning or the like. Then, the base substrate 100and the first bonding layer 104 are brought into close contact with eachother, so that van der Waals force acts on the interface between thebase substrate 100 and the first bonding layer 104, and thus the basesubstrate 100 and the first bonding layer 104 are bonded to each other.By bringing the base substrate 100 and the semiconductor substrate 101into close contact with each other and applying pressure to the bondinginterface therebetween, hydrogen bonds are formed at the bondinginterface, increasing the bonding strength between the first bondinglayer 104 and the base substrate 100. When a silicon oxide film formedby CVD with organic silane is used for the first bonding layer 104, thebase substrate 100 and the first bonding layer 104 can be bonded to eachother at room temperature without heating the base substrate 100 or thesemiconductor substrate 101.

In order to form a good bond, at least one of the surfaces of the basesubstrate 100 and the first bonding layer 104 may be activated beforethey are bonded to each other. In order to activate the surface, thesurface at which a bonding interface is to be formed is irradiated withan atom beam or an ion beam. In that case, it is preferable to generatea neutral atom beam or an ion beam from an inert gas such as argon. Asan alternative method of activation treatment, plasma treatment orradical treatment may also be applied.

After the base substrate 100 and the first bonding layer 104 are broughtinto close contact with each other, heat treatment or pressurizationtreatment can be applied. Applying the heat treatment or pressurizationtreatment can increase the bonding strength. The temperature of the heattreatment is preferably less than or equal to the allowable temperaturelimit of the base substrate 100. The pressurization treatment isperformed such that stress is applied in a direction perpendicular tothe bonding plane, and the pressure applied is determined based on thestrengths of the base substrate 100 and the semiconductor substrate 101.

FIG. 5A is a cross-sectional view for illustrating the step ofseparating a semiconductor layer from the semiconductor substrate 101.First, after bonding the base substrate 100 and the first bonding layer104 to each other, heat treatment for heating the semiconductorsubstrate 101 is applied. By this heat treatment, the volume of minutecavities that are formed in the ion-implanted layer 103 changes, wherebya crack is generated in the ion-implanted layer 103. Therefore, byapplying stress to the semiconductor substrate 101, the semiconductorsubstrate 101 is cleaved along the ion-implanted layer 103, whereby thesemiconductor substrate 101 is separated from the base substrate 100.Accordingly, after the semiconductor substrate 101 is separated from thebase substrate 100, a semiconductor layer 110 which is separated fromthe semiconductor substrate 101 remains fixed on the base substrate 100.

The heat treatment is preferably performed at a temperature of greaterthan or equal to the deposition temperature of the first bonding layer104 and a temperature of less than or equal to the allowable temperaturelimit of the base substrate 100. A heating temperature ranging from 400to 600° C. can generate a crack in the ion-implanted layer 103.Therefore, a substrate with a low allowable temperature limit such as aglass substrate can be used for the base substrate 100.

In addition, since the bonding interface between the base substrate 100and the first bonding layer 104 is heated by this heat treatment,covalent bonds are formed at the bonding interface, and bonding strengthat the bonding interface can be increased.

In FIG. 5A, the top surface of the semiconductor layer 110 is a surfaceon which the ion-implanted layer 103 has cracked. Therefore, theplanarity of the top surface of the semiconductor layer 110 is lowerthan that of the top surface of the semiconductor substrate 101 beforeseparated, and thus irregularities are formed. Therefore, in order torestore the planarity of the top surface of the semiconductor layer 110,the semiconductor layer 110 is irradiated with a laser beam from above.This laser irradiation can also recover the crystallinity of thesemiconductor layer 110. FIG. 5B is a cross-sectional view illustratinga laser irradiation step.

As illustrated in FIG. 5B, the semiconductor layer 110 is irradiatedwith a laser beam 126 from above. Irradiation with the laser beam 126melts the semiconductor layer 110. When the melted portion is cooled andsolidified, a semiconductor layer 102 with improved planarity andcrystallinity is formed. Since the semiconductor layer 110 is heated bythe laser irradiation, a substrate with a low allowable temperaturelimit such as a glass substrate can be used for the base substrate 100.

The irradiation with the laser beam 126 can either partially orcompletely melt the semiconductor layer 110. Note that a state in whichthe semiconductor layer 110 is completely melted means, referring to thestructure of FIG. 5B as an example, a state in which a region of thesemiconductor layer 110 from its top surface to the interface betweenthe semiconductor layer 110 and the first bonding layer 104 is meltedand the melted portion is totally liquefied. Meanwhile, a state in whichthe semiconductor layer 102 is partially melted means a state in which aregion of the semiconductor layer 102 from its top surface to apredetermined depth is melted whereas a solid portion in the otherregion remains. When the semiconductor layer 110 is completely melted bythe irradiation with the laser beam 126, planarization progresses due tothe surface tension of the semiconductor having a liquid phase, and thusthe semiconductor layer 102 with a planarized surface is formed. Inaddition, while the completely melted region of the semiconductor layer110 is being solidified, lateral growth occurs in which crystals of asolid-phase semiconductor in a region adjacent to the melted region growin a lateral direction. When the semiconductor substrate 101 is asingle-crystalline semiconductor substrate, the unmelted portion is asingle-crystalline semiconductor and has uniform crystal orientation.Therefore, crystal grain boundaries are not formed, and thesemiconductor layer 102 obtained through laser irradiation is asingle-crystalline semiconductor layer without crystal grain boundaries.In addition, when the semiconductor layer 110 is partially melted by theirradiation with the laser beam 126, planarization progresses by thesurface tension of the semiconductor having a liquid phase. At the sametime, the liquid-phase portion starts to be cooled by diffusion of heat,so that the semiconductor layer 110 has a temperature gradient in adepth direction. Then, a solid-liquid interface moves from the basesubstrate 100 side to the surface of the semiconductor layer 110,whereby the semiconductor layer 110 is recrystallized. That is, when thesemiconductor layer 110 is partially melted, recrystallizationprogresses starting from the unmelted region of the lower portion, andthus crystals grow in a longitudinal direction. When asingle-crystalline silicon wafer having a main surface with a surfaceorientation of (100) is used as the semiconductor substrate 101, thesemiconductor layer 110 before subjected to laser irradiation is asingle-crystalline silicon layer having a main surface with a surfaceorientation of (100). In addition, the semiconductor layer 102 obtainedby recrystallization of the semiconductor layer 110 by partially orcompletely melting the semiconductor layer 110 through laser irradiationis a single-crystalline silicon layer having a main surface with asurface orientation of (100). That is, when a single-crystallinesemiconductor substrate is used, the laser irradiation step can serve asa planarization step and a recrystallization step.

A laser oscillator that emits the laser beam 126 can be any of acontinuous wave laser, a pseudo-continuous wave laser, and a pulsedlaser. Examples of lasers that are used in the present invention includeexcimer lasers such as a KrF laser and gas lasers such as an Ar laserand a Kr laser. Further, the following solid-state lasers can be used: aYAG laser, a YVO₄ laser, a YLF laser, a YAlO₃ laser, a GdVO₄ laser, aKGW laser, a KYW laser, an alexandrite laser, a Ti:sapphire laser, aY₂O₃ laser, and the like. Although an excimer laser is a pulsed laser, asolid-state laser such as a YAG laser can be used as any of a continuouswave laser, a pseudo-continuous wave laser, and a pulsed laser.

The wavelength of the laser beam is a wavelength absorbed by thesemiconductor layer 110, and can be determined based on the skin depthof the laser beam, the thickness of the semiconductor layer 110, and thelike. For example, the wavelength can be in the range of from 250 to 700nm. In addition, the energy of the laser beam can also be determinedbased on the wavelength of the laser beam, the skin depth of the laserbeam, the thickness of the semiconductor layer 110, and the like. Thepresent inventors have confirmed that the planarity and crystallinity ofthe semiconductor layer 110 can be improved by forming the semiconductorlayer 110 to a thickness of about 170 nm, using a KrF excimer laser forthe laser, and controlling the energy density of the laser beam to bewithin the range of from 300 to 750 mJ/cm². In order to analyze theplanarity and crystallinity of the semiconductor layer 110, observationwith an optical microscope, an AFM (atomic force microscope), and a SEM(scanning electron microscope), observation of EBSP (electron backscatter diffraction patterns), and Raman spectroscopy were conducted. Inaddition, laser irradiation was conducted in the atmospheric airincluding oxygen or in a nitrogen atmosphere not including oxygen. Theplanarity and crystallinity of the semiconductor layer 110 are improvedboth in the atmospheric air and in the nitrogen atmosphere. Note thatthe planarity can be improved more effectively in the nitrogenatmosphere than in the atmospheric air, and also generation of crackscan be suppressed more effectively in the nitrogen atmosphere than inthe atmospheric air.

It is also possible to fix a plurality of semiconductor layers 102 onone base substrate 100. For example, the steps described with referenceto FIGS. 4A to 4C are repeated a plurality of times so that a pluralityof semiconductor substrates 101 are fixed to the base substrate 100.Then, the heat treatment described with reference to FIG. 5A is appliedto separate each semiconductor substrate 101, whereby the plurality ofsemiconductor layers 110 can be fixed to the base substrate 100. Next,the laser irradiation step illustrated in FIG. 5B is applied, so thatthe plurality of semiconductor layers 110 are planarized to form aplurality of semiconductor layers 102.

Next, a method of manufacturing the SOI substrate illustrated in FIG. 2will be described. First, the steps described with reference to FIGS. 4Aand 4B are conducted, so that the ion-implanted layer 103 is formed at aposition of a predetermined depth from the top surface of thesemiconductor substrate 101 as illustrated in FIG. 6A. Then, the firstbonding layer 104 is formed on the top surface of the semiconductorsubstrate 101.

FIG. 6B is a cross-sectional view of the base substrate 100. First, theinsulating layer 105 is formed on the top surface of the base substrate100 as illustrated in FIG. 6B. In order to form a silicon nitride film,for example, plasma CVD may be performed using SiH₄ and NH₃ as a processgas. Alternatively, SiH₄, N₂, and Ar can be used as the process gas. Inaddition, in order to form a silicon oxynitride film or a silicon oxidefilm, plasma CVD may be performed using SiH₄ and N₂O as a process gas.

Next, the second bonding layer 106 is formed on the insulating layer105. A silicon oxide film is formed as the second bonding layer 106.When the second bonding layer 106 is formed using a silicon oxide filmwhich is formed by CVD using an organic silane gas as a silicon sourcegas, the deposition method of the first bonding layer 104 can be otherthan the CVD using an organic silane gas as a silicon source gas. Whenthe semiconductor substrate 101 is a silicon substrate, the firstbonding layer 104 can be formed using a thermal oxide film formed bythermal oxidation. Instead of the thermal oxide film, a chemical oxidelayer formed by chemical oxidation can also be used. Chemical oxide canbe formed by, for example, treating the surface of the silicon substratewith water containing ozone. Since the chemical oxide layer has aboutthe same planarity as the silicon substrate, it is preferable as abonding layer.

FIG. 6C is a cross-sectional view illustrating the step of bonding thesecond bonding layer 106 and the first bonding layer 104 to each otherby bringing the base substrate 100 and the semiconductor substrate 101,which has the first bonding layer 104 formed on its surface, into closecontact with each other. The first bonding layer 104 and the secondbonding layer 106 are bonded to each other through a similar bondingstep to that described with reference to FIG. 4C. When a silicon oxidefilm formed by CVD with organic silane is used for at least one of thefirst bonding layer 104 and the second bonding layer 106, the firstbonding layer 104 and the second bonding layer 106 can be bonded to eachother at room temperature without heating the base substrate 100 or thesemiconductor substrate 101.

At least one of the surfaces of the first bonding layer 104 and thesecond bonding layer 106 is preferably activated before they are broughtinto close contact with each other. The activation may be performed byirradiation with a neutral atom beam of an inert gas such as argon orwith an ion beam of an inert gas. Alternatively, plasma treatment orradical treatment can be performed.

After the first bonding layer 104 and the second bonding layer 106 arebrought into close contact with each other, heat treatment orpressurization treatment can be applied. Applying the heat treatment orpressurization treatment can increase the bonding strength between thefirst bonding layer 104 and the second bonding layer 106. Thetemperature of the heat treatment is preferably less than or equal tothe allowable temperature limit of the base substrate 100. Thepressurization treatment is performed such that stress is applied in adirection perpendicular to a bonding interface, and the pressure appliedis determined based on the strengths of the base substrate 100 and thesemiconductor substrate 101.

FIG. 7A is a cross-sectional view for illustrating the step ofseparating a semiconductor layer from the semiconductor substrate 101.Heat treatment is applied to generate a crack in the ion-implanted layer103, similarly to the heat treatment described with reference to FIG.5A. The bonding interface between the first bonding layer 104 and thesecond bonding layer 106 is heated by this heat treatment. Therefore,covalent bonds are formed at the bonding interface, and bonding strengthat the bonding interface can be increased. By generating a crack in theion-implanted layer 103, the semiconductor substrate 101 is cleavedalong the ion-implanted layer 103, whereby the semiconductor substrate101 and the base substrate 100 can be separated from each other. As aresult, an SOI substrate is formed as illustrated in FIG. 7A in whichthe semiconductor layer 110 separated from the semiconductor substrate101 is fixed on the base substrate 100.

FIG. 7B is a cross-sectional view for illustrating the step ofirradiating the SOI substrate with a laser beam. After the semiconductorsubstrate 101 is separated, the semiconductor layer 110 is irradiatedwith a laser beam 126 from above as in the laser irradiation stepdescribed with reference to FIG. 5B, so that the semiconductor layer 102with a planarized surface and improved crystallinity is formed.

It is also possible to fix a plurality of semiconductor layers 102 onone base substrate 100. For example, the steps described with referenceto FIGS. 6A to 6C are repeated a plurality of times so that a pluralityof semiconductor substrates 101 are fixed to the base substrate 100.Then, the heating step described with reference to FIG. 6A is applied toseparate each semiconductor substrate 101, whereby a plurality ofsemiconductor layers 110 can be fixed to the base substrate 100. Next,the laser irradiation step illustrated in FIG. 7B is applied, so thatthe plurality of semiconductor layers 110 are planarized to form aplurality of semiconductor layers 102.

In the methods of manufacturing the SOI substrates described withreference to FIGS. 4A to 7B, the bonding strength between thesemiconductor layer 102 and the base substrate 100 can be firm even whenthe base substrate is a glass substrate or the like having an allowabletemperature limit of less than or equal to 700° C. For the basesubstrate 100, various glass substrates used in the electronics industrycan be employed, for example, alkali-free glass such as aluminosilicateglass, aluminoborosilicate glass, or barium borosilicate glass. That is,the single-crystalline semiconductor layer can be formed over asubstrate which is over 1 meter on a side. With such a large-areasubstrate, a liquid crystal display or an electroluminescence displaycan be manufactured. In addition, not only such a display device, butalso a semiconductor integrated circuit can be manufactured.

Hereinafter, a method of manufacturing a semiconductor device using anSOI substrate will be described with reference to FIGS. 8A to 9B.Although an SOI substrate with the same structure as the SOI substratein FIG. 1 is used here, an SOI substrate with a different structure canalso be used.

As illustrated in FIG. 8A, the semiconductor layer 102 is provided overthe base substrate 100 with the first bonding layer 104 interposedtherebetween. First, a silicon nitride layer 155 and a silicon oxidelayer 156 are formed in a region corresponding to each element formationregion. The silicon oxide layer 156 is used as a hard mask in etchingthe semiconductor layer 102 for element isolation. The silicon nitridelayer 155 is used as an etching stopper in etching the semiconductorlayer 102. In order to control the threshold voltage, the semiconductorlayer 102 is implanted with a p-type impurity such as boron, aluminum,or gallium or an n-type impurity such as arsenic or phosphorus. Whenboron is used as a p-type impurity, for example, the doping may becontrolled such that the semiconductor layer 102 contains boron at aconcentration of less than or equal to 5×10¹⁷ to 1×10¹⁸ cm⁻³.

FIG. 8B is a cross-sectional view for illustrating the step of etchingthe semiconductor layer 102 and the first bonding layer 104 with thesilicon oxide layer 156 as a mask. Exposed end faces of thesemiconductor layer 102 and the first bonding layer 104 are nitrided byplasma treatment. This nitridation treatment forms silicon nitridelayers 157 on at least peripheral end portions of the semiconductorlayer 102. Silicon nitride has an insulating property as well asoxidation resistance. Therefore, formation of the silicon nitride layers157 can prevent leakage current from the end faces of the semiconductorlayer 102 as well as growth of an oxide film on the end faces, whichcould otherwise produce a bird's beak between the semiconductor layer102 and the first bonding layer 104.

FIG. 8C is a cross-sectional view for illustrating the step ofdepositing an element-isolation insulating layer 158. Theelement-isolation insulating layer 158 is formed by depositing a siliconoxide film by CVD using TEOS and oxygen. As illustrated in FIG. 8C, theelement-isolation insulating layer 158 is deposited to be thick so as tofill a space between the adjacent semiconductor layers 102.

FIG. 8D illustrates the step of partially removing the element-isolationinsulating layer 158 to a depth at which the silicon nitride layer 155is exposed. This removing step can be performed by dry etching orchemical mechanical polishing. The silicon nitride layer 155 serves asan etching stopper. The element-isolation insulating layer 158 partiallyremains so as to fill the space between the adjacent semiconductorlayers 102. After that, the silicon nitride layer 155 is removed.

Next, as illustrated in FIG. 8E, a gate insulating layer 159, a gateelectrode 160 with a two-layer structure, sidewall insulating layers161, first impurity regions 162, second impurity regions 163, and aninsulating layer 164 are formed. By forming the first impurity regions162 and the second impurity regions 163 in the semiconductor layer 102,a channel formation region 165 is formed. The insulating layer 164 isformed with silicon nitride and is used as a hard mask for etching thegate electrode 160.

Next, as illustrated in FIG. 9A, an interlayer insulating layer 166 isformed. The interlayer insulating layer 166 is formed by depositing BPSG(borophosphosilicate glass) and planarizing it through reflowing.Alternatively, the interlayer insulating layer 166 may be formed bydepositing a silicon oxide film using TEOS and planarizing it throughchemical mechanical polishing. In the planarization treatment, theinsulating layer 164 above the gate electrode 160 serves as an etchingstopper. Contact holes 167 are formed in the interlayer insulating layer166. The contact holes 167 each have a self-aligned contact structurewhich is formed by use of the sidewall insulating layer 161.

Next, as illustrated in FIG. 9B, contact plugs 170 are formed by CVDusing tungsten hexafluoride. Further, an insulating layer 171 is formedand openings are formed in positions above the contact plugs 170. Then,wirings 172 are provided in the openings. The wirings 172 are formedwith aluminum or an aluminum alloy. Specifically, the wirings 172 areeach formed with a metal film which has a barrier metal such asmolybdenum, chromium, or titanium as each of top and bottom layers.

In this manner, a field-effect transistor can be fabricated using thesemiconductor layer 102 bonded to the base substrate 100. Since thesemiconductor layer 102 in accordance with this embodiment mode is asingle-crystalline semiconductor having uniform crystal orientation,field-effect transistors with uniform characteristics and highperformance can be provided. That is, it is possible to suppressvariations in threshold voltage, mobility, and the like that are theimportant characteristics of transistors and also to achieve highperformance such as a decrease in threshold voltage and an improvementin mobility.

In addition, since the semiconductor layer 102 is irradiated with alaser beam so that the planarity of the surface of the semiconductorlayer 102 is improved, the interface state density between the channelformation region and the gate insulating layer of the field-effecttransistor can be lowered. Therefore, a field-effect transistor withexcellent characteristics such as low driving voltage, high field-effectmobility, and small subthreshold swing can be formed.

Semiconductor devices for various uses can be manufactured using thefield-effect transistors described with reference to FIGS. 8A to 9B.Hereinafter, specific examples of semiconductor devices will bedescribed with reference to the drawings.

First, a microprocessor will be described as an example of asemiconductor device. FIG. 10 is a block diagram illustrating anexemplary configuration of a microprocessor 200. This microprocessor 200is manufactured using the SOI substrate in accordance with thisembodiment mode as described above.

The microprocessor 200 includes an arithmetic logic unit (also referredto as an ALU) 201, an arithmetic logic unit controller (ALU controller)202, an instruction decoder 203, an interrupt controller 204, a timingcontroller 205, a register 206, a register controller 207, a businterface (bus I/F) 208, a read-only memory (ROM) 209, and a ROMinterface (ROM I/F) 210.

An instruction input to the microprocessor 200 through the bus interface208 is input to and decoded by the instruction decoder 203, and theninput to the ALU controller 202, the interrupt controller 204, theregister controller 207, and the timing controller 205. Each of the ALUcontroller 202, the interrupt controller 204, the register controller207, and the timing controller 205 performs various control operationsbased on the decoded instruction.

Specifically, the ALU controller 202 generates signals for controllingthe operation of the ALU 201. While the microprocessor 200 is executinga program, the interrupt controller 204 processes an interrupt requestfrom an external input/output device or a peripheral circuit based onthe priority of the request or a mask state. The register controller 207generates an address of the register 206 and performs reading or writingdata from/to the register 206 based on the state of the microprocessor200. The timing controller 205 generates signals for controlling theoperation timing of the ALU 201, the ALU controller 202, the instructiondecoder 203, the interrupt controller 204, and the register controller207.

For example, the timing controller 205 has an internal clock generatorwhich generates an internal clock signal CLK 2 based on a referenceclock signal CLK1, and supplies the internal clock signal CLK 2 to thevarious circuits described above. Note that the configuration of themicroprocessor 200 illustrated in FIG. 10 is just a simplified exampleand, in practice, the microprocessor 200 can have a wide variety ofconfigurations depending on its use.

Since the above-described microprocessor 200 has an integrated circuitformed from a single-crystalline semiconductor layer with uniformcrystal orientation (an SOI layer) that is bonded to a substrate with aninsulating surface or an insulating substrate, not only an increase inprocessing speed but also a reduction in power consumption can beachieved.

Described next is an example of a semiconductor device with anarithmetic function which can perform noncontact datatransmission/reception. FIG. 11 is a block diagram illustrating anexemplary configuration of such a semiconductor device. Thesemiconductor device illustrated in FIG. 11 is a computer (hereinafterreferred to as an “RFCPU”) which operates through transmission andreception of signals to/from an external device by radio communication.

As illustrated in FIG. 11, an RFCPU 211 includes an analog circuitportion 212 and a digital circuit portion 213. The analog circuitportion 212 includes a resonant circuit 214 having a resonant capacitor,a rectifier circuit 215, a constant voltage circuit 216, a reset circuit217, an oscillation circuit 218, a demodulation circuit 219, amodulation circuit 220, and a power supply control circuit 230. Thedigital circuit portion 213 includes an RF interface 221, a controlregister 222, a clock controller 223, a CPU interface 224, a centralprocessing unit 225, a random access memory 226, and a read-only memory227.

The operation of the RFCPU 211 with the above-described configuration isas follows. Upon receipt of a signal at the antenna 228, the resonantcircuit 214 generates induced electromotive force. The inducedelectromotive force is stored in a capacitor portion 229 through therectifier circuit 215. This capacitor portion 229 is preferably formedfrom a capacitor such as a ceramic capacitor or an electric double layercapacitor. The capacitor portion 229 does not need to be formed insidethe RFCPU 211 and can be attached as a discrete part to a substrate withan insulating surface that partially constitutes the RFCPU 211.

The reset circuit 217 generates signals for resetting and initializingthe digital circuit portion 213. For example, the reset circuit 217generates a signal, which rises with delay from the time of increase inpower supply voltage, as a reset signal. The oscillation circuit 218changes the frequency and duty ratio of a clock signal based on acontrol signal generated by the constant voltage circuit 216. Thedemodulation circuit 219 is a circuit which demodulates received signalsand the modulation circuit 220 is a circuit which modulates data to betransmitted.

For example, the demodulation circuit 219 is constructed from a low-passfilter and digitalizes an amplitude-shift-keying (ASK) modulated signalreceived, based on changes in amplitude of the signal. The modulationcircuit 220 changes the amplitude of a communication signal by changingthe resonance point of the resonant circuit 214 in order to transmit anASK modulated signal whose amplitude is changed, as transmission data.

The clock controller 223 generates control signals for changing thefrequency and duty ratio of clock signals based on the power supplyvoltage or current consumed by the central processing unit 225. Thepower supply voltage is monitored by the power supply control circuit230.

A signal input to the RFCPU 211 from the antenna 228 is demodulated bythe demodulation circuit 219 and decomposed into a control command,data, and the like by the RF interface 221. The control command isstored in the control register 222. Examples of the control commandinclude a read instruction of data stored in the read-only memory 227, awrite instruction of data into the random-access memory 226, and anarithmetic instruction to the central processing unit 225.

The central processing unit 225 accesses the read-only memory 227, therandom access memory 226, and the control register 222 via the CPUinterface 224. The CPU interface 224 has a function of generating anaccess signal to any of the read-only memory 227, the random accessmemory 226, and the control register 222 based on an address requestedby the central processing unit 225.

The arithmetic method of the central processing unit 225 can be a methodin which an OS (operating system) is stored in the read-only memory 227and a program is read out and executed at the start-up time. It is alsopossible to use a method in which a dedicated arithmetic circuit isprovided so that arithmetic processing is executed in a hardware manner.It is also possible to use a method with both hardware and software, inwhich a part of arithmetic processing is executed with a dedicatedarithmetic circuit whereas the other part of the arithmetic processingis executed with the central processing unit 225 using a program.

Since the above-described RFCPU 211 has an integrated circuit formedfrom a single-crystalline semiconductor layer with uniform crystalorientation (an SOI layer) that is bonded to a substrate with aninsulating surface or an insulating substrate, not only an increase inprocessing speed but also a reduction in power consumption can beachieved. Accordingly, long-time operation can be ensured even when thesize of the capacitor portion 229 for supplying electricity is reduced.

Example 1

The present inventors have confirmed that applying laser irradiation canrecover the crystallinity of a single-crystalline semiconductor layer tothe same level as that of a semiconductor substrate before processed.Further, they have confirmed that the laser irradiation can planarizethe surface of the single-crystalline semiconductor layer.

First, a method of manufacturing an SOI substrate in this example willbe described with reference to FIGS. 12A to 12H. FIGS. 12A to 12H arecross-sectional views illustrating a method of manufacturing the SOIsubstrate. The SOI substrate in this example is a substrate obtained byfixing a single-crystalline layer on a glass substrate.

A single-crystalline silicon wafer 501 is prepared as a semiconductorsubstrate (see FIG. 12A). The conductivity type of the wafer is a ptype, and the resistivity thereof is about 10 Ω·cm. In addition, thecrystal orientation of the main surface is (100).

First, a silicon oxynitride film 502 with a thickness of 100 nm isformed over the top surface of the single-crystalline silicon wafer 501,and a silicon nitride oxide film 503 with a thickness of 50 nm is formedover the silicon oxynitride film 502 (see FIG. 12B). The siliconoxynitride film 502 and the silicon nitride oxide film 503 are formed byconsecutively depositing two films using the same plasma CVD apparatus.The process gas of the silicon oxynitride film 502 is SiH₄ and N₂O, andthe flow rates of SiH₄ and N₂O are 4 sccm and 800 sccm, respectively.The substrate temperature at the deposition step is 400° C. The processgas of the silicon nitride oxide film 503 is SiH₄, NH₃, N₂O, and H₂, andthe flow rates of SiH₄, NH₃, N₂O, and H₂ are 10 sccm, 100 sccm, 20 sccm,and 400 sccm, respectively. The substrate temperature at the depositionstep is 350° C.

Next, in order to form an ion-implanted layer 504 in thesingle-crystalline silicon wafer 501, hydrogen ions 521 are implanted tothe single-crystalline silicon wafer 501 using an ion doping apparatus(see FIG. 12C). A 100% hydrogen gas is used as a source gas, and thehydrogen gas is excited to generate plasma. Ions in the generated plasmaare accelerated with an electric field without mass separation toirradiate the single-crystalline silicon wafer 501, whereby theion-implanted layer 504 is formed. In this example, the implantationstep of hydrogen ions is conducted twice with an accelerating voltage of80 kV and a dosage of 1.0×10¹⁶ ions/cm². By exciting the hydrogen gas inthe ion doping apparatus, three kinds of ion species that are H⁺, H₂ ⁺,and H₃ ⁺ are generated. All of the generated ion species are acceleratedto irradiate the single-crystalline silicon wafer 501, whereby theion-implanted layer 504 is formed.

After the formation of the ion-implanted layer 504, a silicon oxide film505 is formed over the single-crystalline silicon wafer by plasma CVD.TEOS and O₂ are used as a process gas for formation of the silicon oxidefilm 505. The substrate temperature at the deposition step is 300° C.

Next, a base substrate and the single-crystalline silicon wafer 501 arebonded to each other. FIG. 12E is a cross-sectional view forillustrating the bonding step. Here, a glass substrate 500 is used asthe base substrate. The glass substrate 500 is an alkali-free glasssubstrate (product name: AN100) with a thickness of 0.7 mm. The surfaceof the glass substrate 500 and the silicon oxide film 505 formed on thesurface of the single-crystalline silicon wafer 501 are brought into aclose contact with and bonded to each other.

Next, the single-crystalline silicon wafer 501 bonded to the glasssubstrate 500 is heated at 500° C. for two hours, so that thesingle-crystalline silicon wafer 501 is separated along theion-implanted layer 504 as illustrated in FIG. 12F. Accordingly, asingle-crystalline silicon layer 506 remains over the glass substrate500. The thickness of the single-crystalline silicon layer 506 is about170 nm. The glass substrate 500 on which the single-crystalline siliconlayer 506 is fixed with the films 502, 503, and 505 interposedtherebetween will be referred to as an SOI substrate 511. In FIG. 12F, asingle-crystalline silicon layer 507, which represents thesingle-crystalline silicon layer 501 separated from the glass substrate500, is shown.

Next, the single-crystalline silicon layer 506 of the SOI substrate 511is irradiated with a laser beam 522 as illustrated in FIG. 12G. In thelaser irradiation treatment, a XeCl excimer laser which emits a beamwith a frequency of 308 nm is used as a laser oscillator. The laser beam522 has a pulse width of 25 nanoseconds and a repetition rate of 30 Hz.The laser beam on the irradiation plane is condensed into a linear beamwith an optical system and the laser beam 522 scans the irradiationplane in a width direction (a short-axis direction of the beam shape).The SOI substrate 511 is set on a stage of a laser irradiation apparatusand the stage is moved such that the SOI substrate 511 is moved relativeto the laser beam 522 as shown by an arrow 523, whereby thesingle-crystalline silicon layer 506 is scanned by the laser beam 522.Here, the scan rate of the laser beam 522 is set at 1.0 mm/sec. so thatthe same region of the single-crystalline silicon layer 506 isirradiated with about 12 shots of the laser beam 522.

Irradiation with the laser beam 522 is conducted in the atmospheric airor a nitrogen atmosphere. The nitrogen atmosphere is produced byirradiating the single-crystalline silicon layer 506 with the laser beam522 in the atmospheric air and blowing nitrogen to a region of thesingle-crystalline silicon layer 506 which is irradiated with the laserbeam 522.

By irradiating the single-crystalline silicon layer 506 with the laserbeam 522, a single-crystalline silicon layer 508 with planarity andimproved crystallinity is formed (see FIG. 12H). Note that an SOIsubstrate 512 is the SOI substrate 511 after subjected to laserirradiation.

Described next is that the single-crystalline silicon layer 506 isrecrystallized by the laser irradiation.

In this example, EBSP (electron back scatter diffraction patterns) ofthe surfaces of the single-crystalline silicon layer 506 not subjectedto laser irradiation and the single-crystalline silicon layer 508subjected to laser irradiation were measured. FIGS. 13A to 13C are IPF(inverse pole figure) maps obtained from the measured data.

FIG. 13A is an IPF map of the single-crystalline silicon layer 506before subjected to laser irradiation. FIGS. 13B and 13C are IPF maps ofthe single-crystalline silicon layer 508 subjected to laser irradiation.Specifically, FIG. 13B shows the case where laser irradiation isconducted in the atmospheric air, and FIG. 13C shows the case wherelaser irradiation is conducted in a nitrogen atmosphere.

FIG. 13D is a color-code map obtained by color-coding each surfaceorientation of crystals, which illustrates the relationship between thecolors of the IPF map and crystal orientations.

The IPF maps in FIGS. 13A to 13C show that the crystal orientation ofthe single-crystalline silicon layer 506 is not disordered before orafter the laser irradiation, and the surface orientation of thesingle-crystalline silicon layer 506 remains the same as the (100)surface orientation of the single-crystalline silicon wafer 501 whichhas been used. In addition, FIGS. 13A to 13C can confirm that thesingle-crystalline silicon layer 506 has no crystal grain boundariesbefore or after the laser irradiation. This is because each of the IPFmaps in FIGS. 13A to 13C is a square image with one color that is acolor (red in the color drawing) representing the (100) orientation ofthe color-code map in FIG. 13D.

Note that dots that appear in the IPF maps in FIGS. 13A to 13C representportions with a low CI value. A CI value is an index value indicatingthe reliability and accuracy of data that determines crystalorientation. The CI value can be low when there are crystal grainboundaries or defects of crystals. An IPF map with less portions with alow CI value can be evaluated as having a nearly perfect crystalstructure and high crystallinity.

The measurement of EBSP can confirm the following: separating asingle-crystalline silicon wafer whose main surface has (100) surfaceorientation can form the single-crystalline silicon layer 506 whose mainsurface has (100) surface orientation, the surface orientation of themain surface of the single-crystalline silicon layer 508 subjected tolaser irradiation remains (100), and crystal grain boundaries are notformed in the single-crystalline silicon layer 508 by the laserirradiation. That is, the laser irradiation treatment is therecrystallization treatment of the single-crystalline silicon layerseparated from the single-crystalline silicon wafer.

Described next is that the crystallinity of the single-crystallinesilicon layer 506 can be improved by laser irradiation. Here, Ramanspectroscopy was conducted to compare the crystallinity of thesingle-crystalline silicon layer 506 before subjected to laserirradiation and the crystallinity of the single-crystalline siliconlayer 508 subjected to laser irradiation.

FIG. 14A is a graph showing changes in Raman shift vs. laser energydensity. FIG. 14B is a graph showing the FWHM (full width at halfmaximum) of the Raman spectra vs. laser energy density. Note that inFIGS. 14A and 14B, data at an energy density of 0 mJ/cm² is the measureddata of the single-crystalline silicon layer 506 before subjected tolaser irradiation.

The peak wavenumber (also referred to as a peak value) of Raman shift isa value determined by the oscillation mode of crystal lattices, which ispeculiar to a crystal structure. Single-crystalline silicon with nointernal stress has a Raman shift of 520.6 cm⁻¹. Therefore, in FIG. 14A,a peak value of Raman shift which is closer to 520.6 cm⁻¹ means that thecrystal structure of the single-crystalline silicon layer 508 is closerto single-crystalline silicon and thus has good crystallinity. Note thatwhen compressive stress is applied to single crystals, the distancebetween lattices becomes short and, therefore, the peak wavenumbershifts to a high wavenumber side in proportion to the magnitude of thecompressive stress. On the other hand, when tensile stress is applied,the peak wavenumber shifts to a low wavenumber side in proportion to themagnitude of the stress.

In addition, in FIG. 14B, a smaller FWHM indicates more uniformcrystallinity with less fluctuation of crystal state. Commercialsingle-crystalline silicon wafers have an FWHM of about 2.5 to 3.0 cm⁻¹.An FWHM closer to this value can be regarded as a barometer of a uniformcrystal structure like the crystallinity of a single-crystalline siliconwafer.

The measurement results of Raman spectroscopy in FIGS. 14A and 14B canconfirm that applying laser irradiation can recover the crystallinity toabout the same level of crystallinity as that of the single-crystallinesilicon wafer before processed.

Described next is that the surface of a single-crystalline silicon layeris planarized by laser irradiation.

In this example, the surface of a single-crystalline silicon layer of anSOI substrate was observed by taking dark-field images with an opticalmicroscope and images with an atomic force microscope (AFM), in order toevaluate the planarity of the surface of the single-crystalline siliconlayer. Single-crystalline silicon layers that were observed with eachmicroscope include the single-crystalline silicon layer 506 beforesubjected to laser irradiation, the single-crystalline silicon layer 508subjected to laser irradiation in the atmospheric air, and thesingle-crystalline silicon layer 508 subjected to laser irradiation in anitrogen atmosphere. FIG. 15 shows dark-field images observed with anoptical microscope and images observed with an atomic force microscope(hereinafter referred to as AFM images).

Observation of dark-field images with an optical microscope is a methodin which a sample is illuminated with light in an oblique direction toobserve scattered rays and diffraction rays from the sample. Therefore,when the surface of the sample is flat, the observed image is a blackimage (a dark image) because there is no scattering or diffraction ofthe illumination light. For this reason, in this example, the dark-fieldimages are observed in order to evaluate the planarity of thesingle-crystalline silicon layers.

The measurement conditions in using an atomic force microscope (AFM) areas follows:

AFM: a scanning probe microscope (model: SPI3800N/SPA500) manufacturedby Seiko Instruments Inc.

Measurement Mode: a dynamic force mode (DFM mode)

Cantilever: SI-DF40 (made of silicon, a spring constant of 42 N/m, aresonant frequency of 250 to 390 kHz, and a probe having a tip with acurvature of R≦10 nm)

Measured Area: 90 μm×90 μm

Measured points: 256 points×256 points

The DFM mode is a measurement mode in which a cantilever is resonated ata given frequency (a frequency peculiar to the cantilever) and the shapeof the surface of a sample is measured with the distance between theprobe and the sample controlled in such a manner that the oscillationamplitude of the cantilever is maintained constant. Since the surface ofthe sample and the cantilever are not in contact with each other in theDFM mode, it is possible to measure the surface of the sample withoutchanging its original shape or damaging the surface.

Note that the SOI substrates 511 and 512 whose images observed with amicroscope are shown in FIG. 15 are manufactured under partiallydifferent conditions from the SOI substrates 511 and 512 whose data areshown in FIGS. 13A to 14B. Here, in order to distinguish the two typesof substrates, the SOI substrates 511 and 512 whose data are shown inFIG. 15 will be referred to as an SOI substrate 511-2 and an SOIsubstrate 512-2, respectively.

In a manufacture process of the SOI substrate 511-2, the siliconoxynitride film 502 is formed to a thickness of 50 nm in the step ofFIG. 12B. In addition, in order to form the ion-implanted layer 504 inFIG. 12C, the step of adding hydrogen ions is conducted once with ahydrogen-ion accelerating voltage of 40 kV and a dosage of 1.75×10¹⁶ions/cm². In the step of FIG. 12F, the single-crystalline silicon wafer501 is separated through heat treatment at 600° C. for 20 minutes andthen at 650° C. for 6.5 minutes. The thickness of the single-crystallinesilicon layer 506 of the SOI substrate 511-2 is about 120 nm. Note thatthe laser irradiation treatment in FIG. 12G is conducted in a similarway as to the SOI substrate 511 except for the energy density of laserirradiation, so that the SOI substrate 512-2 is formed. FIG. 15 showsthe energy density of laser irradiation for the SOI substrate 511-2.

FIG. 15 shows the surface roughness of the single-crystalline siliconlayers 506 and 508. As the surface roughness, average surface roughnessR_(a), root-mean-square roughness R_(MS), and the distance between thehighest and lowest points P-V (hereinafter referred to as“peak-to-valley distance P-V”) are calculated. These values werecalculated by analyzing the surface roughness of the AFM images shown inFIG. 15, using accessory software of the AFM.

FIG. 15 demonstrates that the single-crystalline silicon layer 506 canbe planarized by laser irradiation. That is, recrystallization of thesingle-crystalline semiconductor layer of the SOI substrate andplanarization of the surface thereof can be performed at the same timeby melting the single-crystalline semiconductor layer through laserirradiation with controlled energy density. In order words,planarization of the single-crystalline silicon layer of the SOIsubstrate can be achieved without applying stress which could break theglass substrate or heating the glass substrate at a temperature of overits strain point.

Hereinafter, the average surface roughness R_(a), the root-mean-squareroughness R_(MS), and the peak-to-valley distance P-V that are used asthe indices of the planarity of a surface in this specification will bedescribed.

The average surface roughness (R_(a)) is an index obtained by expandingthe central line average surface roughness R_(a) that is defined byJISB0601:2001 (ISO4287:1997) into three dimensions so that the index canbe applied to a measured surface. R_(a) can be expressed as the averageof the absolute value of a deviation from a reference surface to aspecified surface and is given by Formula (a1).

$\begin{matrix}{R_{a} = {\frac{1}{S_{0}}{\int_{Y_{1}}^{Y_{2}}{\int_{X_{1}}^{X_{2}}{{{{F\left( {X,Y} \right)} - Z_{0}}}{\mathbb{d}X}{\mathbb{d}Y}}}}}} & ({a1})\end{matrix}$

A measured surface Z is a surface shown by all the measured data, andcan be given by Formula (a2).Z=F(X,Y)  (a2)

In addition, the specified surface is a surface whose roughness is to bemeasured, which is a rectangular region surrounded by four pointsrepresented by coordinates of (X₁, Y₁), (X₁, Y₂), (X₂, Y₁), and (X₂,Y₂). The area of the specified surface which is ideally flat isrepresented by S₀. Therefore, S₀ can be given by Formula (a3).S ₀=(X ₂ −X ₁)·(Y ₂ −Y ₁)  (a3)

In addition, the reference surface is a flat surface represented by Z=Z₀where Z₀ represents the average value of the height of the specifiedsurface. The reference surface is parallel with an X-Y plane. Theaverage value Z₀ can be calculated from Formula (a4).

$\begin{matrix}{Z_{0} = {\frac{1}{S_{0}}{\int_{Y_{1}}^{Y_{2}}{\int_{X_{1}}^{X_{2}}{{F\left( {X,Y} \right)}{\mathbb{d}X}{\mathbb{d}Y}}}}}} & ({a4})\end{matrix}$

The root-mean-square roughness (R_(MS)) is an index obtained byexpanding R_(MS) for a profile curve into three dimensions similarly toR_(a) so that the index can be applied to a measured surface. R_(MS) canbe expressed as the square root of the mean of the square of a deviationfrom a reference surface to a specified surface, and can be given byFormula (a5).

$\begin{matrix}{R_{m\; s} = \sqrt{\frac{1}{S_{0}}{\int_{Y_{1}}^{Y_{2}}{\int_{X_{1}}^{X_{2}}{\left\{ {{F\left( {X,Y} \right)} - Z_{0}} \right\}^{2}{\mathbb{d}X}{\mathbb{d}Y}}}}}} & ({a5})\end{matrix}$

The peak-to-valley distance P-V can be expressed as a difference betweena peak (the highest point) Z_(max) and a valley (the lowest point)Z_(min) of a specified surface, and can be given by Formula (a6).P−V=Z _(max) −Z _(min)  (a6)

The peak and the valley herein are obtained by expanding the “peak” andthe “valley” defined in JISB0601:2001 (ISO4287:1997) into threedimensions, and the peak is expressed as the highest point in aprotrusion of a specified surface, whereas the valley is expressed asthe lowest point in the specified surface.

Example 2

A method of forming an ion-implanted layer is described below in Example2.

The formation of the ion-implanted layer is conducted by irradiation ofa semiconductor substrate with accelerated ions, and the ions arederived from hydrogen (H) (hereafter referred to as “hydrogen ionspecies”). More specifically, a hydrogen gas or a gas which containshydrogen in its composition is used as a source gas (a source material);a hydrogen plasma is generated by exciting the source gas; and asemiconductor substrate is irradiated with the hydrogen ion species inthe hydrogen plasma. In this manner, the ion-implanted layer is formedin the semiconductor substrate.

(Ions in Hydrogen Plasma)

In such a hydrogen plasma as described above, hydrogen ion species suchas H⁺, H₂ ⁺, and H₃ ⁺ are present. Here are listed reaction equationsfor reaction processes (formation processes, destruction processes) ofthe hydrogen ion species.e+H→e+H ⁺ +e  (1)e+H ₂ →e+H ₂ ⁺ +e  (2)e+H ₂ →e+(H ₂)*→e+H+H  (3)e+H ₂ ⁺ →e+(H ₂ ⁺)*→e+H ⁺ +H  (4)H ₂ ⁺ +H ₂ →H ₃ ⁺ +H  (5)H ₂ ⁺ +H ₂ →H ⁺ +H+H ₂  (6)e+H ₃ ⁺ →e+H ⁺ +H+H  (7)e+H ₃ ⁺ →H ₂ +H  (8)e+H ₃ ⁺ →H+H+H  (9)

FIG. 16 is an energy diagram which schematically shows some of the abovereactions. Note that the energy diagram shown in FIG. 16 is merely aschematic diagram and does not depict the relationships of energies ofthe reactions exactly.

[H₃ ⁺ Formation Process]

As shown above, H₃ ⁺ is mainly produced through the reaction processthat is represented by the reaction equation (5). On the other hand, asa reaction that competes with the reaction equation (5), there is thereaction process represented by the reaction equation (6). For theamount of H₃ ⁺ to increase, at the least, it is necessary that thereaction of the reaction equation (5) occur more often than the reactionof the reaction equation (6) (note that, because there are also otherreactions, (7), (8), and (9), through which the amount of H₃ ⁺ isdecreased, the amount of H₃ ⁺ is not necessarily increased even if thereaction of the reaction equation (5) occurs more often than thereaction of the reaction equation (6)). In contrast, when the reactionof the reaction equation (5) occurs less often than the reaction of thereaction equation (6), the proportion of H₃ ⁺ in a plasma is decreased.

The amount of increase in the product on the right-hand side (rightmostside) of each reaction equation given above depends on the density of asource material on the left-hand side (leftmost side) of the reactionequation, the rate coefficient of the reaction, and the like. Here, itis experimentally confirmed that, when the kinetic energy of H₂ ⁺ islower than about 11 eV, the reaction of the reaction equation (5) is themain reaction (that is, the rate coefficient of the reaction equation(5) is sufficiently higher than the rate coefficient of the reactionequation (6)) and that, when the kinetic energy of H₂ ⁺ is higher thanabout 11 eV, the reaction of the reaction equation (6) is the mainreaction.

A force is exerted on a charged particle by an electric field, and thecharged particle gains kinetic energy. The kinetic energy corresponds tothe amount of decrease in potential energy due to an electric field. Forexample, the amount of kinetic energy a given charged particle gainsbefore colliding with another particle is equal to a potential energythat was lost by travel of the charged particle. That is, in a situationwhere a charged particle can travel a long distance in an electric fieldwithout colliding with another particle, the kinetic energy (or theaverage thereof) of the charged particle tends to be higher than that ina situation where the charged particle cannot. Such a tendency toward anincrease in kinetic energy of a charged particle can be shown in asituation where the mean free path of a particle is long, that is, in asituation where pressure is low.

Even in a situation where the mean free path is short, the kineticenergy of a charged particle may be high if the charged particle cangain a high amount of kinetic energy while traveling through the path.That is, it can be said that, even in the situation where the mean freepath is short, the kinetic energy of a charged particle is high if thepotential difference between two points is large.

This is applied to H₂ ⁺. Assuming that an electric field is present asin a plasma generation chamber, the kinetic energy of H₂ ⁺ is high in asituation where the pressure inside the chamber is low and the kineticenergy of H₂ ⁺ is low in a situation where the pressure inside thechamber is high. That is, because the reaction of the reaction equation(6) is the main reaction in the situation where the pressure inside thechamber is low, the amount of H₃ ⁺ tends to be decreased, and becausethe reaction of the reaction equation (5) is the main reaction in thesituation where the pressure inside the chamber is high, the amount ofH₃ ⁺ tends to be increased. In addition, in a situation where anelectric field in a plasma generation region is high, that is, in asituation where the potential difference between given two points islarge, the kinetic energy of H₂ ⁺ is high. In the opposite situation,the kinetic energy of H₂ ⁺ is low. That is, because the reaction of thereaction equation (6) is the main reaction in the situation where theelectric field is high, the amount of H₃ ⁺ tends to be decreased, andbecause the reaction of the reaction equation (5) is the main reactionin a situation where the electric field is low, the amount of H₃ ⁺ tendsto be increased.

[Differences Depending on Ion Source]

Here, an example, in which the proportions of ion species (particularly,the proportion of H₃ ⁺) are different, is described. FIG. 17 is a graphshowing the results of mass spectrometry of ions that are generated froma 100% hydrogen gas (with the pressure of an ion source of 4.7×10⁻² Pa).The horizontal axis represents ion mass. In the spectrum, the mass 1peak, the mass 2 peak, and the mass 3 peak correspond to H⁺, H₂ ⁺, andH₃ ⁺, respectively. The vertical axis represents the intensity of thespectrum, which corresponds to the number of ions. In FIG. 17, thenumber of ions with different masses is expressed as a relativeproportion where the number of ions with a mass of 3 is defined as 100.It can be seen from FIG. 17 that the ratio between ion species that aregenerated from the ion source, i.e., the ratio between H⁺, H₂ ⁺, and H₃⁺, is about 1:1:8. Note that ions at such a ratio can also be generatedby an ion doping apparatus which has a plasma source portion (ionsource) that generates a plasma, an extraction electrode that extractsan ion beam from the plasma, and the like.

FIG. 18 is a graph showing the results of mass spectrometry of ions thatare generated from PH₃ when an ion source different from that for thecase of FIG. 17 is used and the pressure of the ion source is about3×10⁻³ Pa. The results of this mass spectrometry focus on the hydrogenion species. In addition, the mass spectrometry was performed bymeasurement of ions that were extracted from the ion source. As in FIG.17, the horizontal axis of FIG. 18 represents ion mass, and the mass 1peak, the mass 2 peak, and the mass 3 peak correspond to H⁺, H₂ ⁺, andH₃ ⁺, respectively. The vertical axis represents the intensity of aspectrum corresponding to the number of ions. It can be seen from FIG.18 that the ratio between ion species in a plasma, i.e., the ratiobetween H⁺, H₂ ⁺, and H₃ ⁺, is about 37:56:7. Note that, although FIG.18 shows the data obtained when the source gas is PH₃, the ratio betweenthe hydrogen ion species is almost the same when a 100% hydrogen gas isused as a source gas, as well.

In the case of the ion source from which the data shown in FIG. 18 isobtained, H₃ ⁺, of H⁺, H₂ ⁺, and H₃ ⁺, is generated at a proportion ofonly about 7%. On the other hand, in the case of the ion source fromwhich the data shown in FIG. 17 is obtained, the proportion of H₃ ⁺ canbe up to 50% or higher (about 80% according to data of FIG. 17). This isthought to result from the pressure and electric field inside a chamber,which is clearly shown in the consideration of [H₃ ⁺ Formation Process].

[H₃ ⁺ Irradiation Mechanism]

When a plasma that contains a plurality of ion species as shown in FIG.17 is generated and a semiconductor substrate is irradiated with thegenerated ion species without any mass separation being performed, thesurface of the semiconductor substrate is irradiated with each of H⁺, H₂⁺, and H₃ ⁺ ions. In order to reproduce the mechanism, from theirradiation with ions to the formation of an ion-implanted layer, thefollowing five types of models (Models 1 to 5) are considered.

Model 1, where the ion species used for irradiation is H⁺, which isstill H⁺ (H) after the irradiation.

Model 2, where the ion species used for irradiation is H₂ ⁺, which isstill H₂ ⁺ (H₂) after the irradiation.

Model 3, where the ion species used for irradiation is H₂ ⁺, whichsplits into two H atoms (H⁺ ions) after the irradiation.

Model 4, where the ion species used for irradiation is H₃ ⁺, which isstill H₃ ⁺ (H₃) after the irradiation.

Model 5, where the ion species used for irradiation is H₃ ⁺, whichsplits into three H atoms (H⁺ ions) after the irradiation.

[Comparison of Simulation Results with Measured Values]

Based on the above models 1 to 5, the irradiation of an Si substratewith hydrogen ion species was simulated. As simulation software, SRIM(the Stopping and Range of Ions in Matter) was used. The SRIM issimulation software for ion introduction processes by a Monte Carlomethod and is an improved version of TRIM (the Transport of Ions inMatter). Note that SRIM is software intended for amorphous structures,but SRIM can be applied to cases where irradiation with the hydrogen ionspecies is performed with high energy at a high dose. This is becausethe crystal structure of an Si substrate changes into anon-single-crystal structure due to the collision of the hydrogen ionspecies with Si atoms.

Simulation results are shown below. In the simulation of this example, acalculation based on Model 2 was performed with the H₂ ⁺ replaced by H⁺that has twice the mass. Furthermore, a calculation based on Model 3 wasperformed with the H₂ ⁺ replaced by H⁺ that has half the kinetic energy,a calculation based on Model 4 was performed with the H₃ ⁺ replaced byH⁺ that has three times the mass, and a calculation based on Model 5,with the H₃ ⁺ replaced by H⁺ that has one-third the kinetic energy.

Distribution of a hydrogen element (H) in a depth direction wascalculated in cases where a Si substrate was irradiated with thehydrogen ion species (irradiation with 100,000 atoms for H) ataccelerating voltage of 80 kV using Models 1 to 5. FIG. 19 shows thecalculation results. In FIG. 19, measured values of the distribution inthe depth direction of a hydrogen element (H) included in the Sisubstrate are also shown. The measured values are data measured by SIMS(Secondary Ion Mass Spectroscopy) (hereinafter, referred to as SIMSdata). The sample measured by SIMS was a Si substrate which wasirradiated with hydrogen ion species (H⁺, H₂ ⁺, H₃) produced under theconditions for measuring data of FIG. 17, at accelerating voltage of 80kV.

In FIG. 19, the vertical axis of the graph of the measured values usingthe Models 1 to 5 is a right vertical axis showing the number ofhydrogen atoms. The vertical axis of the graph of the SIMS data is aleft vertical axis showing hydrogen concentration. The horizontal axisof the graph of the measured values and the SIMS data represents a depthfrom the surface of the Si substrate.

If the SIMS data, which is measured values, is compared with thecalculation results, Models 2 and 4 obviously do not match the peaks ofthe SIMS data in the graph and a peak corresponding to Model 3 cannot beobserved in the SIMS data. This shows that the contribution of each ofModels 2 to 4 is comparatively smaller than those of Models 1 and 5.Considering that the kinetic energy of ions is on the order ofkiloelectron volts whereas the H—H bond energy is only about severalelectron volts, it is thought that the contribution of each of Models 2and 4 is small because H₂ ⁺ and H₃ ⁺ mostly split into H⁺ or H bycolliding with Si atoms.

Accordingly, Models 2 to 4 will not be considered hereinafter. Next aredescribed the simulation results obtained when a Si substrate wasirradiated with the hydrogen ion species (irradiation with 100,000 atomsfor H) at accelerating voltage of 80 kV, 60 kV and 40 kV, using Models 1and 5.

FIGS. 20 to 22 each show the calculation result in a depth direction ofhydrogen (H) included in the Si substrate. FIG. 20 shows the case wherethe accelerating voltage is 80 kV; FIG. 21, the case where theaccelerating voltage is 60 kV; and FIG. 22, the case where theaccelerating voltage is 40 kV. Further, in FIGS. 20 to 22, SIMS data asa measured value and a fitting graph to the SIMS data (hereinafter, alsoreferred to as a fitting function) are also shown. The sample measuredby SIMS was a Si substrate which was irradiated with hydrogen ionspecies (H⁺, H₂ ⁺, H₃ ⁺) produced under the conditions for measuringdata of FIG. 17, at accelerating voltage of 80 kV, 60 kV or 40 kV. Notethat the calculation values obtained using Models 1 and 5 are expressedon the vertical axis (right vertical axis) as the number of hydrogenatoms, and the SIMS data and the fitting function are expressed on thevertical axis (left vertical axis) as the concentration of hydrogenatoms. The horizontal axis represents depth from the surface of a Sisubstrate in the graph.

The fitting function is obtained using the calculation formula (b-1)given below, in consideration of Models 1 and 5. Note that, in thecalculation formula (b-1), X and Y represent fitting parameters and Vrepresents volume.[Fitting Function]=X/V×(Data of Model 1)+Y/V×(Data of Model 5)  (b-1)

For determining of the fitting function, in consideration of the ratiobetween ion species used for actual irradiation (H⁺:H₂ ⁺:H₃ ⁺ is about1:1:8, FIG. 17), the contribution of H₂ ⁺ (i.e., Model 3) should also beconsidered; however, the contribution of H₂ ⁺ is excluded from theconsideration given here for the following reasons:

Because the amount of hydrogen introduced through the irradiationprocess represented by Model 3 is lower than that introduced through theirradiation process of Model 5, there is no significant influence evenif Model 3 is excluded from the consideration (no peak corresponding toModel 3 appears in the SIMS data either, FIG. 19).

The contribution of Model 3 is likely to be obscured by channeling(movement of atoms due to crystal lattice structure) that occurs in theirradiation process of Model 5, because the peak position in the profileof Model 3 is close to that of Model 5 (FIG. 19). That is, it isdifficult to estimate fitting parameters for Model 3. This is becausethis simulation assumes amorphous Si and the influence due tocrystallinity is not considered.

FIG. 23 lists the fitting parameters of the calculation formula (b-1).At any of the accelerating voltages, the ratio of the amount of Hintroduced to the Si substrate according to Model 1 to that introducedaccording to Model 5 is about 1:42 to 1:45 (the amount of H in Model 5,when the amount of H in Model 1 is defined as 1, is about 42 to 45), andthe ratio between ion species used for irradiation in the number, H⁺(Model 1) to that of H₃ ⁺ (Model 5) is about 1:14 to 1:15 (the amount ofH₃ ⁺ in Model 5, when the amount of H⁺ in Model 1 is defined as 1, isabout 14 to 15). Considering that Model 3 is not considered and thecalculation assumes amorphous Si, it can be said that the ratio shown inFIG. 23 is close to that of the ratio between hydrogen ion species usedfor actual irradiation (H⁺:H₂ ⁺:H₃ ⁺ is about 1:1:8, FIG. 17) isobtained.

[Effects of Use of H₃ ⁺]

A plurality of benefits resulting from H₃ ⁺ can be enjoyed byirradiation of a substrate with hydrogen ion species with a higherproportion of H₃ ⁺ as shown in FIG. 17. For example, because H₃ ⁺ splitsinto H⁺, H, or the like to be introduced into a substrate, ionintroduction efficiency can be improved compared with the case ofirradiation mainly with H⁺ or H₂ ⁺. This leads to an improvement in SOIsubstrate production efficiency. In addition, because the kinetic energyof H⁺ or H after H₃ ⁺ splits similarly tends to be low, H₃ ⁺ is suitablefor manufacture of thin semiconductor layers.

Note that, in this example, a method is described in which an ion dopingapparatus that is capable of irradiation with the hydrogen ion speciesas shown in FIG. 17 is used in order to efficiently perform irradiationwith H₃ ⁺. Ion doping apparatuses are inexpensive and excellent for usein large-area treatment. Therefore, by irradiation with H₃ ⁺ by use ofsuch an ion doping apparatus, significant effects such as an improvementin semiconductor characteristics, and an increase in area, a reductionin costs, and an improvement in production efficiency of SOI substratescan be obtained. On the other hand, if first priority is given toirradiation with H₃ ⁺, there is no need to interpret the presentinvention as being limited to the use of an ion irradiation apparatus.

This application is based on Japanese Patent Application serial no.2007-112140 filed with Japan Patent Office on Apr. 20, 2007, the entirecontents of which are hereby incorporated by reference.

1. A method of manufacturing an SOI substrate, comprising the steps of:forming an ion introduced layer in a semiconductor substrate; forming asilicon oxide film on the semiconductor substrate by chemical vapordeposition using organic silane as a silicon source gas; bonding thesemiconductor substrate to a base substrate with the silicon oxide filminterposed therebetween; heating the semiconductor substrate to separatea part of the semiconductor substrate at the ion introduced layer,thereby, forming a semiconductor layer on the base substrate; andirradiating the semiconductor layer with a laser beam having an energydensity within the range of from 300 to 750 mJ/cm² so that thesemiconductor layer is melted at least partly, wherein the ionintroduced layer is formed by using a halogen gas as a source gas,irradiating the semiconductor substrate with the ions generated from thehalogen gas, and then using a hydrogen gas as a source gas, andirradiating the semiconductor substrate with the ions generated from thehydrogen gas.
 2. The method of manufacturing an SOI substrate accordingto claim 1, further comprising a step of forming an insulating layer onthe semiconductor substrate before forming the ion introduced layer. 3.The method of manufacturing an SOI substrate according to claim 2,wherein the insulating layer is a single-layer film including at leastone of a silicon nitride film and a silicon nitride oxide film or amulti-layer film formed by stacking two or more films.
 4. The method ofmanufacturing an SOI substrate according to claim 1, wherein the ionintroduced layer is formed by exciting a source gas containing one ormore gasses selected from the group consisting of a hydrogen gas, anoble gas, a halogen gas, and a halogen compound gas to generate ionsand irradiating the semiconductor substrate with the ions.
 5. The methodof manufacturing an SOI substrate according to claim 4, wherein the ionintroduced layer is formed in the semiconductor substrate before formingthe silicon oxide film.
 6. The method of manufacturing an SOI substrateaccording to claim 5, wherein a heating temperature for forming thesilicon oxide film is less than or equal to 350° C. and a heatingtemperature for separating the part of the semiconductor substrate ismore than or equal to 400° C.
 7. The method of manufacturing an SOIsubstrate according to claim 5, wherein a heating temperature forforming the silicon oxide film is a temperature at which ions that havebeen introduced to the ion introduced layer do not escape, and a heatingtemperature for separating the part of the semiconductor substrate is atemperature at which the ions that have been introduced to the ionintroduced layer escape.
 8. The method of manufacturing an SOI substrateaccording to claim 4, wherein the ion introduced layer is formed bymass-separating the ions generated from the source gas and irradiatingthe semiconductor substrate with mass-separated ions.
 9. The method ofmanufacturing an SOI substrate according to claim 1, wherein the ionintroduced layer is formed by exciting a hydrogen gas to generate ionsincluding H₃ ⁺ ions and irradiating the semiconductor substrate with theions.
 10. A method of manufacturing an SOI substrate, comprising thesteps of: forming an ion introduced layer in a semiconductor substrate;forming a bonding layer on the semiconductor substrate; bonding thesemiconductor substrate to a base substrate with the bonding layerinterposed therebetween; heating the semiconductor substrate to separatea part of the semiconductor substrate at the ion introduced layer,thereby, forming a semiconductor layer on the base substrate; andirradiating the semiconductor layer with a laser beam having an energydensity within the range of from 300 to 750 mJ/cm² so that thesemiconductor layer is melted at least partly, wherein the ionintroduced layer is formed by using a halogen gas as a source gas,irradiating the semiconductor substrate with the ions generated from thehalogen gas, and then using a hydrogen gas as a source gas, andirradiating the semiconductor substrate with the ions generated from thehydrogen gas, and wherein the ions generated from the hydrogen gasinclude H₃ ⁺ ions.
 11. The method of manufacturing an SOI substrateaccording to claim 10, further comprising a step of forming aninsulating layer on the semiconductor substrate before forming the ionintroduced layer.
 12. The method of manufacturing an SOI substrateaccording to claim 11, wherein the insulating layer is a single-layerfilm including at least one of a silicon nitride film and a siliconnitride oxide film or a multi-layer film formed by stacking two or morefilms.
 13. The method of manufacturing an SOI substrate according toclaim 10, wherein the ion introduced layer is formed in thesemiconductor substrate before forming the bonding layer.
 14. The methodof manufacturing an SOI substrate according to claim 13, wherein aheating temperature for forming the bonding layer is less than or equalto 350° C. and a heating temperature for separating the part of thesemiconductor substrate is more than or equal to 400° C.
 15. The methodof manufacturing an SOI substrate according to claim 13, wherein aheating temperature for forming the bonding layer is a temperature atwhich ions that have been introduced to the ion introduced layer do notescape, and a heating temperature for separating the part of thesemiconductor substrate is a temperature at which the ions that havebeen introduced to the ion introduced layer escape.
 16. The method ofmanufacturing an SOI substrate according to claim 10, wherein thegenerated ions further include H⁺ ions and H₂ ⁺ ions, and wherein thepercentage of H₃ ⁺ in the total amount of H⁺, H₂ ⁺, and H₃ ⁺ is greaterthan or equal to 70%.